Python: proportional editing vertex move
look at the doc: http://www.blender.org/api/blender_python_api_2_76_release/bpy.ops.transform.html?highlight=proportional#bpy.ops.transform.transform

By the way you can look in the 'action log' of the info editor (window header). enlarge it, sroll down, select entry it with your select mouse button and use CtrlC to copy the command for your action